1. Field of the Invention
The present invention relates to antimicrobial lubricant compositions, and to their use, for example, to treat or lubricate containers and/or conveyor systems for containers. The invention also relates to containers and conveyor systems treated with an antimicrobial lubricant.
2. Description of Related Art
Containers are receptacles in which materials are or will be held or carried. Containers are commonly used in the food or beverage industry to hold food or beverages. Often lubricants are used in conveying systems for containers, to ensure the appropriate movement of containers on the conveyor.
In the commercial distribution of many products, including most beverages, the products are packaged in containers of varying sizes. The containers can be in the form of cartons, cans, bottles, Tetra Pak.RTM. packages, waxed carton packs, and other forms of containers. In most packaging operations, the containers are moved along conveying systems, usually in an upright position, with the opening of the container facing vertically up or down. The containers are moved from station to station, where various operations, such as filling, capping, labeling, sealing, and the like, are performed.
Containers, in addition to their many possible formats and constructions, may comprise many different types of materials, such as metals, glasses, ceramics, papers, treated papers, waxed papers, polymeric materials, composites, and layered structures. Any desired polymeric materials can be used, such as polyolefins, including polyethylene, polypropylene, polystyrene, and mixtures thereof, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) and mixtures thereof, polyamides, polycarbonates, and the like. Also, containers, such as bottles, with layered, laminated films, formed from PEN, PET, copolymers of the monomers that form PEN and PET, or mixtures thereof, can be used. Containers can be coated with internal and/or external coatings, formed by, for example, thermosetting or UV curing, such as epoxy polymers cured with amines.
Lubricating solutions are often used on conveying systems during the filling of containers, for example, with beverages. There are a number of different properties that are desirable for such lubricants. For example, the lubricant should provide an acceptable level of lubricity for the system. It is also desirable that the lubricants have a viscosity which allows it to be applied by conventional pumping and/or application apparatus, such as by spraying, roll coating, wet bed coating, and the like, commonly used in the industry.
In the beverage industry, there is a high demand for conveyor lubricants that are beverage compatible, and have both lubricative and antimicrobial properties. By beverage compatible, is meant that the lubricant is compatible with the beverage so that it does not form solid deposits when it accidentally contacts spilled beverages on the conveyor system. This property is important since the formation of deposits on the conveyor system may change the lubricity of the system and could require shut-down of the equipment to facilitate cleaning.
Carbonated beverages contain ingredients with anionic charges, such as colors and flavors, which are held in solution through emulsification. Given this generally negative charge, the cationic constituents of a synthetic lubricant, such as quaternary ammonium salts, amines, and ether amines, may react with the beverages to form precipitates. The precipitates accumulate on conveyors, housing, and floors as a tenacious soil, and may cause a halt in production to facilitate cleaning.
If the lubricant is for use on PET bottle lines, then good compatibility with PET is desired. Currently, containers, including PET bottles, and/or the conveying system are often coated with an aqueous-based lubricant to provide lubricity to the container so that it can more easily travel down a conveyor system. Many currently used aqueous-based lubricants are disadvantageous because they are incompatible with many beverage containers, such as PET and other polyalkylene terephthalate containers, and may lead to stress cracking and rupture of the PET bottles.
A sufficient lubrication of the conveyor ensures a proper movement of containers along the conveyor system. Lubricants having fatty acids are known to have good lubricity, especially for metal surface lubrication. However, fatty acids generally need to be neutralized in order to have a good solubility in water. The use of sodium or potassium hydroxide as the neutralizing agent, in fatty acid containing lubricants, has been found to increase the alkalinity of the lubricant, and to thus contribute and promote the stress cracking in PET containers.
PET bottle manufacturers and soft drink bottlers have come to a growing understanding that alkalinity is one root cause of stress crack failure of pressurized PET containers. As a result, alkalinity limits of less than 100 ppm as CaCO.sub.3 have been proscribed for any water or lubricant that comes into contact with the PET article. This development has led to the obsolescence of many longstanding lubricant technologies. For example, as discussed above, fatty acid based lubricants require neutralization with alkaline materials in order to achieve water solubility of the product. The resultant alkalinity of fatty acid products as applied to the conveyors and bottles often exceed the current alkalinity limit. It is also believed that PET stress cracking can be promoted by certain types of lubricant additives, such as alkyl(ether)(di)amines and quaternary ammonium salts.
Lubricants generally contain an antimicrobial agent to reduce the growth of microbes. Antimicrobial agents are agents that eliminate or inactivate microorganisms, or prevent, frustrate, or reduce the growth of microorganisms. Because conveyor lubricants are often used at low concentration, the antimicrobial agent should preferably be highly water soluble and effective at very diluted solutions. Although some types of alcohols, amines, and quaternary ammonium salts are known to satisfy these requirements, they are often disadvantageous because their incompatibility with PET containers can enhance the PET stress cracking.
Also, there are generally known antimicrobial, beverage compatible conveyor lubricants, that contain a quaternary ammonium antimicrobial agent and phosphate esters. Such compositions often are disadvantageous because certain ratios of the components may contribute to soiling due to the mixing of quaternary ammonium compound with soft drink spillage.